Update mysql record and pass id - php

Question

My form is:
<form class="form-horizontal" action="update.php?id=<?php echo $id ?>" method="post">
$sql = 'SELECT * FROM prekes WHERE pirkejo_id=' . $pirkejas . '';
$q = $pdo->prepare($sql);
$prekes = array();
foreach ($pdo->query($sql) as $row) {
if ($row['prek_pav'] != '') {
array_push($prekes, $row);
}
}?>
<input name="prekes[1][pavadinimas]" type="text" value="<?php echo $prekes[0]['prek_pav']?>">
<input name="prekes[1][kaina]" type="text" value="<?php echo $prekes[0]['prek_kaina'] ?>">
<input name="prekes[2][pavadinimas]" type="text"value="<?php echo $prekes[1]['prek_pav']?>">
<input name="prekes[2][kaina]" type="text" value="<?php echo $prekes[1]['prek_kaina'] ?>">
I dont know how to optimize it. I want to update my records in database and have no idea how to pass prekes_id value to UPDATE sql.
I found that My update updates all records with the last value from my form. all recors are same as last entered.
$pdo = Database::connect();
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$sql = "UPDATE customers set name = ?, pavarde = ?, ak = ?, numeris = ? WHERE id = ?";
$q = $pdo->prepare($sql);
$q->execute(array($name, $pavarde, $ak, $numeris, $id));
foreach ($prekes as $preke) {
$sql = "UPDATE prekes SET prek_pav= ?,prek_kaina=? WHERE prekes_id=".$preke['prekes_id'];
$q = $pdo->prepare($sql);
$q->execute(array($preke['pavadinimas'], $preke['kaina']));
}
Database::disconnect();
header("Location: default.php");
I use this code to solve this. Are there any better working solution to this problem?
My table prekes (prekes_id, pirkejo_id, prek_pav, prek_kaina). I take pirkejo_id from $_POST['id'].